Fe-cr-ni-al ferritic alloys

Abstract

Fe-Cr-Ni-Al ferritic alloy capable of forming hot oxidation/corrosion resistive aluminum oxide scale in the surface thereof by exposure to oxidation environments at elevated temperatures. Due to the ferritic structure, the aluminum oxide scale is formed uniformly and densely to improve scale adherence, or prevent scale flaking. The mechanical properties of the ferritic alloy is considerably improved by incorporation of controlled amounts of Cr, Ni, and Al relative to each other, which are added to precipitate minute Ni-Al intermetallic compounds in the alloy matrix while retaining the ferritic structure. Such minute Ni-Al intermetallic compounds are thought to be responsible for improved mechanical properties, including high temperature strength, tensile strength, hardness and the like. Whereby, the alloy combine excellent hot oxidation/corrosion resistance and improved mechanical properties.

What is claimed is: 
     
       1. An Fe-Cr-Ni-Al ferritic alloy capable of forming an aluminum oxide scale in the surface thereof in hot oxidation environments, said alloy consisting essentially of by weight: 25 to 30 percent chromium;   15 to 25 percent nickel;   4 to 8 percent aluminum;   0.05 to 1.0 percent at least one element selected from the group consisting of zirconium, hafnium, cerium, lanthanum, neodymium, gadolinium; not more than 0.1 percent yttrium; and   balance iron, wherein the alloy has a content ratio (chromium and aluminum) to nickel above the solid line of FIG. 2.   
     
     
       2. An Fe-Cr-Ni-Al ferritic alloy capable of forming an aluminum oxide scale in the surface thereof in hot oxidation environments, said alloy consisting essentially of by weight: 25 to 35 percent chromium;   15 to 25 percent nickel;   4 to 8 percent aluminum;   not more than 0.5 percent titanium;   0.05 to 1.0 percent at least one element selected from the group consisting of zirconium, hafnium, cerium, lanthanum, neodymium, gadolinium; not more than 0.1 percent yttrium; and   balance iron.   
     
     
       3. The alloy of claim 1, wherein the alloy has a single ferritic phase, or consists substantially solely of ferritic phase. 
     
     
       4. The alloy of claim 2, wherein the alloy has a content ratio of (chromium and aluminum) to nickel above the solid line of FIG. 2.